My first fat adapted cycling failure

(david czech) #101

Probably a dumb question from me,
but here it is anyway:

How do these tests determine what percentage of your output is being driven by fat burning rather than other fuel sources?


Without getting tested in a lab setting, I don’t think you can measure your fat grams per minute burned. But the adapted athletes do show the ability to get energy from fat at a much much higher rate. It’s clear that the path to getting there is not a clear one with all the individual differences out there.

(Greg Borchert) #103

The testing I have had is Active Metabolic Assessment. I had my test at my gym, which is LifeTime Fitness. They have the equipment and capability, and during their 60 Day Challenge periods it goes for under $100. Normally it’s $249 I think. But, there are lots of places around the country that do VO2 Max or VO2 Metabolic Testing, which is the same thing. Sports clinics at colleges and universities would be one source.

What the test reveals is percentage of fat vs glucose burning in various heart rate zones, among other things like calories per minute burned in different zones, as well as VO2 Max.

It is useful information to have. I haven’t done a repeat test yet, but I will do so. The idea is that as you have a longer history in fat adaptation, you will burn a higher percentage of fat at higher levels of exertion.

(david czech) #104

The percentage of fat v glucose by HR sounds like great information to have.

I still want to figure out how they can derive that from VO2.

It seems like they would have to measure for some other byproducts of the reaction, but maybe the percentage of oxygen utilized is measurably different depending on fat/glucose ratio?

(CharleyD) #105

This is it. your Respiratory Quotient or Respiratory Exchange Ratio is the tell-tale since you need less 02 to burn fat for the same amount of energy than if glucose is your main substrate.

If keto-adapted, you can still burn sugar but it’s at a higher heart rate.

(mark whittaker) #106

I have been keto for a little over 3 months. I have been doing long hilly rides with just UCAN and a few eggs in advance. I have a 100 mile race with 8000 ft of climbing coming ng up this weekend. I am thinking about storing some extra glycogen a few days in advance. And sticking to ucan on the race. Will this kill my fat addaption during the race? Or give me the energy I need for the hills?

Last weekend I did 70 mi with 5000 ft of climbing
I ate some pasta the night before ( first real carbs since starting keto). I felt like total shit during the ride and barely finished. I blame it on the pasta. I think maybe it reduced my fat burning ability for the next day.

2 weeka prior I did 80 miles with 6k ft clbing and felt fine.( No pasta night before). But since on keto I am much slower up the hills.

I am concerned that I won be able to get through this race in a reasonable amount of time without some more carbs for the climbs. But also worried that the carbs will destroy my performance since my body is no longer used to them. Any advice for me?


If you’re like me, at 3 months you are a “tweener”, meaning you’re about halfway adapted to burn fat in a performance setting. You can ride all day in a fasted state if low intensity, but may bonk when you dial it up. It’s kind of a crap shoot as to whether you will have a good day.

I think the risk is in eating high glycemic load carbs, throwing you completely out of ketosis. However, my opinion and experience has been that UCAN superstarch seems to work as advertised, giving you a slow carb drip, allowing you to burn carbs and fat at the same time. I think the trick is to have carbs two nights before, top off your glycogen stores, and start the morning of the event in ketosis and with low insulin. Eat the superstarch about an hour before start. Also, you will need to give yourself 20-30 minutes of low intensity warm-up to bring all your energy online.

A lot of overthinking, but when it works, it’s pretty amazing.

(mark whittaker) #108

This is the exact approach that I took and it seem to work very well but at Mile 50 I started eating high-glycemic carbs and I ended up doing fine the only problem I had was starting at about mile 40 I had extreme leg cramps on the flats on the climbs had no leg pain the flats we’re tough

(ianrobo) #109

I got cramps when thought no chance of being dehydrated etc so did a lot of research. There is actually so much out there about it and some of it very contradictory … but I read something that nothing to do with salts and if you feel it just stretch. So I had it again shortly afterwards, stretched and fine afterwards.

The real lesson I took away is to stretch your legs at every chance possible

(Ryan Thompson) #110

Love all the great comments on this thread. I’ve been doing keto for two months, dropped a lot of weight and doing some winter fat biking here in MN all with the intent to ride hard next summer…hopefully as fat adapted. I’m concerned that my version of road cycling is anaerobic, the typical 90-minute group ride where at the end things get competitive and we are racing. I’m concerned fat adapted isn’t going to cut it and by the comments I’m reading and interpreting as fat adapted mean on aerobic only, not for racing. I love keto and IF, but cycling is more important both physically and socially, so any help on how to overcome this hurdle is appreciated!

(ianrobo) #111

Well Ryan, you have a choice IMHO.

if you are basically doing 90 mins at high HR levels Keto may gave you a base but you will be burning carbs, but never use them all up. In other words you will be slower to access the carbs and feel like a loss of power and you will need to carb cycle.

Keto will still massively help you overall in the performance but you will need to work out you plans for the races, pros who do do keto will carb cycle before and during the race.

(Jacqui ) #112

I rode again on Sunday being on strict Keto for 10 days, but normally following a mix of keto/low carb lifestyle. The second time I had to walk up the hills after being strict keto. I felt like my brake was stuck on my wheel. I couldn’t ride fast. I didn’t feel light headed thank God.
this Sunday I am going to have a few carbs before the ride, but stay keto for the rest of the time. I think we have to do what works.